1. Field of the Invention
The present invention relates to compound manual transmissions and shift control therefor. In particular, the present invention relates to a manual transmission comprising a two-speed splitter section, a two-speed subsplitter section, and a two-speed range section, all connected in series with a two-forward speed main section, and including a first four-position button type control for selecting the desired splitter/subsplitter ratio combination and a second two-position button type control for selecting the desired range ratio whereby only two lever positions are required to go from start-from-stop to maximum vehicle speed.
2. Description of the Prior Art
Mechanical change gear transmissions, i.e., transmissions providing a plurality of selectable gear ratios between the input and output members thereof, which ratios are selected by the engagement and the disengagement of positive (i.e. jaw type), or predominantly positive clutches, are well known in the prior art.
Compound change gear transmissions of the type having one or more auxiliary sections connected in series with a main transmission section are well known in the prior art. Briefly, by utilizing main and auxiliary sections connected in series, assuming proper sizing of the ratio steps, the total of available transmission ratios is equal to the product of the main and transmission section ratios.
Auxiliary transmission sections are of three general types: range type, splitter type or combined range/splitter type.
In compound transmissions having a range type auxiliary section, the range ratio step or steps are greater than the total ratio coverage of the main transmission section and the main transmission section is shifted progressively through its ratios in each range. Examples of compound transmissions having range type auxiliary sections may be seen by reference to U.S. Pat. Nos. 3,105,395 and 2,637,222, the disclosures of which are hereby incorporated by reference.
In compound transmissions having a splitter type auxiliary section, the ratio steps of the splitter auxiliary section are smaller than the ratio steps of the main transmission section and each main transmission section ratio is split, or subdivided, by a splitter section. In the case of a plurality of splitter auxiliary sections, one of the splitter type auxiliary sections will be a subsplitter type auxiliary section having ratio steps smaller than that in the splitter type auxiliary section and the ratio steps in the splitter type auxiliary section will be split or subdivided by the ratio steps of the subsplitter auxiliary section. Examples of compound change gear transmissions having splitter type auxiliary sections may be seen by reference to U.S. Pat. Nos. 4,290,555; 3,799,002; 4,440,037 and 4,527,447, the disclosures of which are hereby incorporated by reference.
In a combined range and splitter type auxiliary section, or sections, both range and splitter type ratios are provided allowing the main section to be progressively shifted through its ratio in at least two ranges and also allowing the main section ratios to be split in at least one of the ranges. Examples of compound change gear transmissions having a single combined range/splitter type auxiliary section may be seen by reference to U.S. Pat. Nos. 3,648,546 and 4,754,665 and 4,788,889, the disclosures of which are hereby incorporated by reference.
It should be noted that the terms "main" and "auxiliary sections" are relative in that that the designations of the main and auxiliary sections are reversed, the type of auxiliary section (either range or splitter) would also be reversed. In other words, given what is conventionally considered a four-speed main section with two-speed range type auxiliary section, if the normally designated auxiliary is considered the main section, the normally designated main section would be considered a four-speed splitter type auxiliary section therefor.
By generally accepted transmission industry convention, and as used in this description of the invention, the main transmission section of a compound transmission is that section which usually contained the largest (or at least no less) number of forward speed ratios, which allows selection of the neutral position, which contains the reverse ratio(s) and/or which is shifted (in manual or semi-automatic transmissions) by manipulation of a shift bar or shift rail or shift shaft/shift finger assembly as opposed to master/slave valve/cylinder arrangements or the like.
The use of a two-speed input section for a compound transmission utilizing friction clutch devices having a first and a second selectable position for engaging a selected one of two selectable reduction input ratios, and having a third disengaged position allowing the input section to provide the torque brake function normally provided by a master clutch, is known as may be seen by reference to U.S. Pat. No. 4,831,894, the disclosure of which is hereby incorporated by reference.
While the prior art compound change gear transmissions of the type having both range and splitter type auxiliary section gearing are well received and widely used in manually shifted heavy duty vehicles, these and other types of prior art compound change gear transmissions are not totally satisfactory for all applications as a great deal of skill and attention is required to properly operate same as a significant number of the gear ratio changes require movement of the shift lever and manipulation of the vehicle master clutch as opposed to the relatively easier to accomplish splitter only type shifts.
Additionally, attempts to utilize two or more multiple speed splitter sections in series have required at least partial automation and/or complicated and expensive sequencing devices to assure that the multiplicity of clutches to be engaged and disengaged occurs in an acceptable sequence.